The present invention relates generally to methods for manufacturing fiber optic connectors. More particularly, the present invention relates to methods for polishing fiber optic connectors to improve the performance characteristics of the connectors.
Fiber optic connectors are used to terminate the ends of fiber optic cables. There are many different fiber optic connector types. Example types of fiber optic connectors include FC-type, SC-type, ST-type and D4-type.
FIG. 1 shows a typical connector 10. A ferrule 12 is located inside the connector 10. The ferrule 12 is a relatively long, thin cylinder preferably made of a material such as ceramic. Other materials such as metal or plastic can also be used to make the ferrule 12. The ferrule 12 defines a central opening 14 sized to receive a fiber 16 of a given cladding diameter. An epoxy is typically placed into the opening 14 prior to inserting the fiber 16 to hold the fiber 16 in place. The ferrule 12 functions to align and center the fiber 16, as well as to protect it from damage.
Referring still to FIG. 1, the ferrule 12 is supported within a connector body 18 typically made of a material such as metal or plastic. The connector body 18 is typically bonded to fiber optic cable 20 (e.g., the cable 20 can include a reinforcing layer made of a material such as Kevlar that is affixed to the connector 18). A strain relief boot 22 protects the junction between the connector 18 and the cable 20.
Two connectors are preferably interconnected through the use of an adapter 24. Adapter 24 includes a sleeve 26 sized to receive the ferrules of the connectors desired to be connected. For example, ferrule 12 of connector 10 is inserted into a first end 28 of the sleeve 26, while a ferrule (not shown) of a connector desired to be connected to the connector 10 is inserted into a second end 30 of the sleeve 26. As so inserted, the ends of the ferrules abut one another within the sleeve 26 such that their corresponding fibers are held in alignment with one another.
Parameters for evaluating the performance of a connector include insertion loss and return loss. Insertion loss is the measurement of the amount of power that is transferred through a coupling from an input fiber to an output fiber. Return loss is the measurement of the amount of power that is reflected back into the input fiber.
If the back reflection is too great (minimum return loss), it can interfere with the operation of the light source (particularly in single mode systems). Therefore, it is important to minimize the back reflection. For instance, a single mode interconnection with flat end finish can have a return loss of 11 dB which means the return loss is 11 dB down from the incident energy. In other words, if 500 microwatts of energy reaches the fiber end, 40 microwatts would be reflected back. By assuring fiber to fiber contact (eliminating air between the fibers), the return loss can be lowered to over 30 dB which means 500 microwatts would reflect only 0.5 microwatts. The return loss can be even further lowered by polishing the ends of the ferrules to have a rounded polish instead of a flat finish. By round polishing the ends of ferrules, the telecommunications industry has been able to consistent meet the minimum specification of 50 to 55 decibels.
FIG. 2 is a block diagram showing the steps of a convention ferrule polishing technique for providing a rounded ferrule tip. During a first polishing step 70, a hackle of the fiber and residue epoxy are removed from the ferrule tip typically by a hand-sanding process. After the hackle and epoxy have been removed, the tip of the ferrule is machine polished using two or more polishing films (e.g., of varying coarseness) so as to more precisely form an apex and radius into the tip of the ferrule (see step 72). Next, the tip of the ferrule is machine polished with a final polish film as indicated by step 74. During the polishing process, an index layer is formed at the tip of the fiber within the ferrule. The index layer has undesirable optical properties. Thus, at final step 76, the tip of the ferrule is polished with a cerium oxide film causing the fiber to be recessed slightly into the ferrule a distance sufficient to remove the index layer.
One aspect of the present invention relates to a fiber optic connector polishing method that yields connectors having improved operating parameters.
A variety of advantages of the invention will be set forth in part in the description that follows, and in part will be apparent from the description, or may be learned by practicing the invention. It is to be understood that both the foregoing general description and the following detailed description are exemplary and explanatory only and are not restrictive of the invention as claimed.